And so he does: all 31 pages, enumerating rights and responsibilities of “the boyfriend” and “the girlfriend.”

Skimming it, Amy remarks dryly, “It’s so romantic.”

“Mutual indemnification always is, “ he replies.

Joke? No joke.

As news spread of the recent wedding of Mark Zuckerberg, the Facebook billionaire, and Priscilla Chan, the recently graduated medical student, one aspect of their courtship has drawn scrutiny from the chatterati. Years earlier, before Ms. Chan moved to Palo Alto, Calif., to be near Mr. Zuckerberg, the couple forged a relationship agreement in which she insisted on at least one date night and 100 minutes together a week, not in his apartment or at the Facebook office.

Such agreements are hardly common. But many couples do make contracts, written or oral, delineating the idiosyncratic needs of their relationship: how much time they need to spend together and apart; who cooks and who cleans; who feeds the fish. Some turn to couples’ counselors, some hammer out such agreements themselves (as did Ms. Chan and Mr. Zuckerberg, apparently), and others even resort to lawyers. Such discussions expose a couple’s vulnerabilities, and make clear how each partner wants to be heard and understood.

“Each party has a chance to draw a line in the sand or negotiate,” said Kelly M. Roberts, a marriage and family therapist in Oklahoma City. “It’s not based on economic earnings but on relationship capital.”

These are different from prenuptial agreements, which are used to protect marital assets in case of death or divorce. By contrast, relationship agreements can read like wish lists: a business plan for a successful romance. And unlike prenups, which have been challenged in court, most lawyers think that such agreements generally are legally unenforceable.

“It’s more about acknowledging the seriousness of the discussion,” said Cheryl Lynn Hepfer, a matrimonial lawyer in Bethesda, Md. “People’s memories fail. So they say, ‘Remember when this was so important to us that we signed, with witnesses?’ ”

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Lawyers say these contracts are a stripped-down version of cohabitation agreements, which gay men and lesbians in particular began writing years ago when states prohibited same-sex marriage. Those agreements, which protected finances, often enumerated relational requirements.

Ken Altshuler, a lawyer from Portland, Me., who is president of the American Academy of Matrimonial Lawyers, said that in one cohabitation agreement he drafted, a partner prone to seasickness allowed his partner to take one cruise-ship vacation a year, alone.

In return, the seasick-prone partner could not “berate or complain” about cruises, including such digs as blasting the theme from “The Love Boat.”

Cohabitation agreements are now also used by heterosexual couples who may not envision marriage. An agreement might stipulate, for example, that if one partner sets aside graduate studies to work to support the other while finishing up school, then eventually they must reverse roles.

“The issues haven’t changed, but how we’re framing them has,” said Paul Hokemeyer, a Manhattan therapist. “Women are saying: ‘I have a place in the world. I won’t just wait around and expect you to be kind and generous. Let’s nail this down.’ ”

Even just documenting the emotional quid pro quos of a relationship has value, couples’ therapists said. The process forces people to confront issues that might otherwise fester.

Relationship agreements also have contemporary currency because they can be used to “dtr,” texting shorthand for “define the relationship.” And once a couple has worked out their latest terms to “dtr,” they can post a status update on Facebook.

A version of this article appears in print on May 27, 2012, on Page ST9 of the New York edition with the headline: Just Call It A Pre-Prenup. Order Reprints|Today's Paper|Subscribe